317 lines
9.8 KiB
C
317 lines
9.8 KiB
C
/* Alias_irc.c intercepts packages contain IRC CTCP commands, and
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changes DCC commands to export a port on the aliasing host instead
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of an aliased host.
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For this routine to work, the DCC command must fit entirely into a
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single TCP packet. This will usually happen, but is not
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guaranteed.
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The interception is likely to change the length of the packet.
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The handling of this is copied more-or-less verbatim from
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ftp_alias.c
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This software is placed into the public domain with no restrictions
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on its distribution.
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Initial version: Eivind Eklund <perhaps@yes.no> (ee) 97-01-29
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Version 2.1: May, 1997 (cjm)
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Very minor changes to conform with
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local/global/function naming conventions
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withing the packet alising module.
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*/
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/* Includes */
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#include <ctype.h>
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#include <stdio.h>
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#include <string.h>
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#include <sys/types.h>
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#include <netinet/in_systm.h>
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#include <netinet/in.h>
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#include <netinet/ip.h>
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#include <netinet/tcp.h>
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#include <limits.h>
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#include "alias_local.h"
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/* Local defines */
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#define DBprintf(a)
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void
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AliasHandleIrcOut(struct ip *pip, /* IP packet to examine */
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struct alias_link *link, /* Which link are we on? */
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int maxsize /* Maximum size of IP packet including headers */
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)
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{
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int hlen, tlen, dlen;
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struct in_addr true_addr;
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u_short true_port;
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char *sptr;
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struct tcphdr *tc;
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int i; /* Iterator through the source */
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/* Calculate data length of TCP packet */
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tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
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hlen = (pip->ip_hl + tc->th_off) << 2;
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tlen = ntohs(pip->ip_len);
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dlen = tlen - hlen;
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/* Return if data length is too short - assume an entire PRIVMSG in each packet. */
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if (dlen<sizeof(":A!a@n.n PRIVMSG A :aDCC 1 1a")-1)
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return;
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/* Place string pointer at beginning of data */
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sptr = (char *) pip;
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sptr += hlen;
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maxsize -= hlen; /* We're interested in maximum size of data, not packet */
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/* Search for a CTCP command [Note 1] */
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for( i=0; i<dlen; i++ ) {
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if(sptr[i]=='\001')
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goto lFOUND_CTCP;
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}
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return; /* No CTCP commands in */
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/* Handle CTCP commands - the buffer may have to be copied */
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lFOUND_CTCP:
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{
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char newpacket[65536]; /* Estimate of maximum packet size :) */
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int copyat = i; /* Same */
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int iCopy = 0; /* How much data have we written to copy-back string? */
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unsigned long org_addr; /* Original IP address */
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unsigned short org_port; /* Original source port address */
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lCTCP_START:
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if( i >= dlen || iCopy >= sizeof(newpacket) )
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goto lPACKET_DONE;
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newpacket[iCopy++] = sptr[i++]; /* Copy the CTCP start character */
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/* Start of a CTCP */
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if( i+4 >= dlen ) /* Too short for DCC */
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goto lBAD_CTCP;
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if( sptr[i+0] != 'D' )
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goto lBAD_CTCP;
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if( sptr[i+1] != 'C' )
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goto lBAD_CTCP;
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if( sptr[i+2] != 'C' )
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goto lBAD_CTCP;
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if( sptr[i+3] != ' ' )
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goto lBAD_CTCP;
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/* We have a DCC command - handle it! */
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i+= 4; /* Skip "DCC " */
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if( iCopy+4 > sizeof(newpacket) )
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goto lPACKET_DONE;
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newpacket[iCopy++] = 'D';
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newpacket[iCopy++] = 'C';
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newpacket[iCopy++] = 'C';
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newpacket[iCopy++] = ' ';
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DBprintf(("Found DCC\n"));
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/* Skip any extra spaces (should not occur according to
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protocol, but DCC breaks CTCP protocol anyway */
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while(sptr[i] == ' ') {
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if( ++i >= dlen) {
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DBprintf(("DCC packet terminated in just spaces\n"));
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goto lPACKET_DONE;
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}
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}
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DBprintf(("Transferring command...\n"));
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while(sptr[i] != ' ') {
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newpacket[iCopy++] = sptr[i];
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if( ++i >= dlen || iCopy >= sizeof(newpacket) ) {
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DBprintf(("DCC packet terminated during command\n"));
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goto lPACKET_DONE;
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}
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}
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/* Copy _one_ space */
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if( i+1 < dlen && iCopy < sizeof(newpacket) )
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newpacket[iCopy++] = sptr[i++];
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DBprintf(("Done command - removing spaces\n"));
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/* Skip any extra spaces (should not occur according to
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protocol, but DCC breaks CTCP protocol anyway */
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while(sptr[i] == ' ') {
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if( ++i >= dlen ) {
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DBprintf(("DCC packet terminated in just spaces (post-command)\n"));
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goto lPACKET_DONE;
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}
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}
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DBprintf(("Transferring filename...\n"));
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while(sptr[i] != ' ') {
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newpacket[iCopy++] = sptr[i];
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if( ++i >= dlen || iCopy >= sizeof(newpacket) ) {
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DBprintf(("DCC packet terminated during filename\n"));
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goto lPACKET_DONE;
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}
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}
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/* Copy _one_ space */
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if( i+1 < dlen && iCopy < sizeof(newpacket) )
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newpacket[iCopy++] = sptr[i++];
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DBprintf(("Done filename - removing spaces\n"));
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/* Skip any extra spaces (should not occur according to
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protocol, but DCC breaks CTCP protocol anyway */
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while(sptr[i] == ' ') {
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if( ++i >= dlen ) {
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DBprintf(("DCC packet terminated in just spaces (post-filename)\n"));
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goto lPACKET_DONE;
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}
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}
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DBprintf(("Fetching IP address\n"));
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/* Fetch IP address */
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org_addr = 0;
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while(i<dlen && isdigit(sptr[i])) {
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if( org_addr > ULONG_MAX/10UL ) { /* Terminate on overflow */
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DBprintf(("DCC Address overflow (org_addr == 0x%08lx, next char %c\n", org_addr, sptr[i]));
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goto lBAD_CTCP;
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}
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org_addr *= 10;
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org_addr += sptr[i++]-'0';
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}
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DBprintf(("Skipping space\n"));
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if( i+1 >= dlen || sptr[i] != ' ' ) {
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DBprintf(("Overflow (%d >= %d) or bad character (%02x) terminating IP address\n", i+1, dlen, sptr[i]));
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goto lBAD_CTCP;
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}
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/* Skip any extra spaces (should not occur according to
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protocol, but DCC breaks CTCP protocol anyway, so we might
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as well play it safe */
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while(sptr[i] == ' ') {
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if( ++i >= dlen ) {
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DBprintf(("Packet failure - space overflow.\n"));
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goto lPACKET_DONE;
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}
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}
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DBprintf(("Fetching port number\n"));
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/* Fetch source port */
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org_port = 0;
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while(i<dlen && isdigit(sptr[i])) {
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if( org_port > 6554 ) { /* Terminate on overflow (65536/10 rounded up*/
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DBprintf(("DCC: port number overflow\n"));
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goto lBAD_CTCP;
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}
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org_port *= 10;
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org_port += sptr[i++]-'0';
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}
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/* Skip illegal addresses (or early termination) */
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if( i >= dlen || (sptr[i] != '\001' && sptr[i] != ' ') ) {
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DBprintf(("Bad port termination\n"));
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goto lBAD_CTCP;
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}
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DBprintf(("Got IP %lu and port %u\n", org_addr, (unsigned)org_port));
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/* We've got the address and port - now alias it */
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{
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struct alias_link *dcc_link;
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struct in_addr destaddr;
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true_port = htons(org_port);
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true_addr.s_addr = htonl(org_addr);
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destaddr.s_addr = 0;
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/* Steal the FTP_DATA_PORT - it doesn't really matter, and this
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would probably allow it through at least _some_
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firewalls. */
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dcc_link = FindUdpTcpOut (true_addr,
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destaddr,
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true_port,
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0, IPPROTO_TCP);
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DBprintf(("Got a DCC link\n"));
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if ( dcc_link ) {
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struct in_addr alias_address; /* Address from aliasing */
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u_short alias_port; /* Port given by aliasing */
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#ifndef NO_FW_PUNCH
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/* Generate firewall hole as appropriate */
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PunchFWHole(dcc_link);
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#endif
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alias_address = GetAliasAddress(link);
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iCopy += snprintf(&newpacket[iCopy],
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sizeof(newpacket)-iCopy,
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"%lu ", (u_long)htonl(alias_address.s_addr));
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if( iCopy >= sizeof(newpacket) ) { /* Truncated/fit exactly - bad news */
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DBprintf(("DCC constructed packet overflow.\n"));
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goto lBAD_CTCP;
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}
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alias_port = GetAliasPort(dcc_link);
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iCopy += snprintf(&newpacket[iCopy],
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sizeof(newpacket)-iCopy,
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"%u", htons(alias_port) );
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/* Done - truncated cases will be taken care of by lBAD_CTCP */
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DBprintf(("Aliased IP %lu and port %u\n", alias_address.s_addr, (unsigned)alias_port));
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}
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}
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/* An uninteresting CTCP - state entered right after '\001' has
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been pushed. Also used to copy the rest of a DCC, after IP
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address and port has been handled */
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lBAD_CTCP:
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for(; i<dlen && iCopy<sizeof(newpacket); i++,iCopy++) {
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newpacket[iCopy] = sptr[i]; /* Copy CTCP unchanged */
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if(sptr[i] == '\001') {
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goto lNORMAL_TEXT;
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}
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}
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goto lPACKET_DONE;
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/* Normal text */
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lNORMAL_TEXT:
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for(; i<dlen && iCopy<sizeof(newpacket); i++,iCopy++) {
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newpacket[iCopy] = sptr[i]; /* Copy CTCP unchanged */
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if(sptr[i] == '\001') {
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goto lCTCP_START;
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}
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}
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/* Handle the end of a packet */
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lPACKET_DONE:
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iCopy = iCopy > maxsize-copyat ? maxsize-copyat : iCopy;
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memcpy(sptr+copyat, newpacket, iCopy);
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/* Save information regarding modified seq and ack numbers */
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{
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int delta;
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SetAckModified(link);
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delta = GetDeltaSeqOut(pip, link);
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AddSeq(pip, link, delta+copyat+iCopy-dlen);
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}
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/* Revise IP header */
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{
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u_short new_len;
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new_len = htons(hlen + iCopy + copyat);
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DifferentialChecksum(&pip->ip_sum,
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&new_len,
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&pip->ip_len,
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1);
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pip->ip_len = new_len;
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}
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/* Compute TCP checksum for revised packet */
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tc->th_sum = 0;
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tc->th_sum = TcpChecksum(pip);
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return;
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}
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}
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/* Notes:
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[Note 1]
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The initial search will most often fail; it could be replaced with a 32-bit specific search.
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Such a search would be done for 32-bit unsigned value V:
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V ^= 0x01010101; (Search is for null bytes)
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if( ((V-0x01010101)^V) & 0x80808080 ) {
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(found a null bytes which was a 01 byte)
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}
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To assert that the processor is 32-bits, do
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extern int ircdccar[32]; (32 bits)
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extern int ircdccar[CHAR_BIT*sizeof(unsigned int)];
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which will generate a type-error on all but 32-bit machines.
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[Note 2] This routine really ought to be replaced with one that
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creates a transparent proxy on the aliasing host, to allow arbitary
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changes in the TCP stream. This should not be too difficult given
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this base; I (ee) will try to do this some time later.
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*/
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